The present invention relates to an image forming apparatus adapted for use as, for example, an electrophotographic color copying machine of the tandem type.
An electrophotographic color copying machine of the tandem type comprises a plurality of image forming sections that are arranged in the direction of paper transportation. Each image forming section includes a photoconductor drum and a developing unit, which are integrally unitized to form a process unit.
A plurality of drive motors are arranged on the back surface side in the body of the copying machine. A drum shaft of each photoconductor drum is releasably connected for rotation to a drive shaft of its corresponding drive motor.
Toner images of different colors are formed individually on the photoconductor drums of the process unit. The toner images of the individual colors on the drums are transferred successively to the surface of paper that is transported by means of a transfer belt, whereupon a color image is formed on the paper.
The process unit requires maintenance operation after the formation of every tens of thousands of images. Accordingly, the process unit is designed so that it can be loaded into or unloaded from the copying machine body. In starting the maintenance operation, therefore, the process unit can be drawn out of the machine body.
When the process unit is inserted into the color copying machine, the respective drum shafts of its photoconductor drums are connected individually to the respective drive shafts of the drive motors. This connection should be reliable.
The rotation of the drive motors is subject to unevenness or vibration. If the uneven or vibratory rotation is transmitted to the drum shafts of the photoconductor drums through the drive shafts, the resulting images are blurred and lowered in quality.
As is described in Jpn. Pat. Appln. KOKAI Publications Nos. 2-130562, 2-225862, 2-287577, and 3-80264, therefore, arrangements are conventionally used such that a drum shaft and a drive shaft are connected to each other by means of a non-coaxial spur or helical gear train.
Although the drum shaft and the drive shaft can be securely connected to each other in the conventional arrangements, however, the non-coaxial gear train is used for the connection, so that backlash is entailed. Infinitesimal vibration is generated even in helical gears in which impact is dispersed between their teeth. This vibration is transmitted to the photoconductor drums, thereby exerting a bad influence upon the image quality.
In order to solve this problem, a novel arrangement has been developed in which a drum shaft and a drive shaft are coaxially connected to each other by means of a coupling.
In the case of this coupling system, however, the drum shaft cannot be inserted into the coupling if there is relative dislocation between the drum shaft and the drive shaft. In the case of the tandem type, in particular, a plurality of drum shafts are designed to be inserted individually into a plurality of couplings, so that smooth insertion is difficult.
If the drum shaft of a photoconductor drum is inserted into the coupling by force, moreover, images are subject to dimensional unevenness or blur, and excessive load acts on the bearing of the drum shaft. Thus, the bearing is deteriorated, so that satisfactory image quality cannot be ensured.